"Up to now the impact of damaged nerves ... on ED has been underestimated," says study researcher Consuelo Valles-Antuna, of the Hospital Universitario Central de Asturias in Oviedo, Spain, in a news release.

The Spanish study of 90 men found that nearly 69% with sexual problems had nerve damage, mostly peripheral nerve damage.

Men who reported more symptoms and showed more signs of nerve damage also reported more severe symptoms of sexual dysfunction and impotence. In previous research, heart disease and stroke were the most commonly found risk factors for ED.

The results should be read with caution, says Tobias S. Kohler, MD, MPH, a spokesman for the American Urological Association and an assistant professor of urology at Southern Illinois University School of Medicine. He reviewed the study for WebMD but was not involved in it.

While the study results may give doctors some valuable information, he says, ''this is a small study that talks about a correlation. That's a long way from a cause."

About half of American men over age 40 have some degree of ED, according to the American Urological Association.

The study is published in the British Journal of Urology International.

Tracking Nerve Damage

The researchers asked 90 men with impotence, average age 54, questions that gauged the severity of erectile function and tested nerve damage. They used these to determine how often the two conditions occurred together.

ED was classified as severe, moderate, or mild.

The combination of tests and information from patients helped the researchers determine that nerve damage was very common in the men with ED.

The findings suggests that doctors should do nerve studies on patients with ED, Valles-Antuna says in a news release.

"Maybe this is something we need to think about as a potentially [separate] risk factor for ED," Kohler says. "However, these guys had more than just peripheral neuropathy [nerve damage]. They had a lot of other risk factors."

"They didn't rule out all the other risk factors," he says. To say the nerve damage caused the ED is too strong, he says.

Among the risk factors for ED, according to the American Urological Association, are: